Sealand

The Principality of Sealand is a micronation that claims as its territory Roughs Tower as well as territorial waters in a twelve nautical mile radius. Roughs Tower is a former Maunsell Sea Fort located in the North Sea 10 km off the coast of Essex, UK.
HM Fort Roughs was constructed by the UK during World War II in 1942.
It is comprised of a floating pontoon base with a superstructure of two hollow towers joined by a deck . The location chosen was in international waters, outside the then three-mile territorial water claim of the UK.